In Laser Cartilage Reshaping (LCR), shape change is accomplished by first mechanically deforming the tissue and then heating it rapidly using a laser to approximately 60-70 degrees C. Using LCR, cartilages in the head and neck may be reshaped into new stable geometries without the need for cutting or suturing to relieve and/or balance the intrinsic forces that resist deformation. The specific objectives of this proposal include: 1) determining both the acute and long-term mechanical stability of laser irradiated cartilage grafts, 2) characterizing the critical relationship between mechanical stress behavior in response to heat generation in cartilage, 3) developing a finite element model (FEM) to simulate thermoviscoelasticity in cartilage in order to perform parametric analysis, and 4) correlating shape change with viability and laser dosimetry. These aims complement and extend the objectives outlined in the P.l.'s existing K-08 MCSDA. Cell/tissue culture techniques and an in vivo rabbit model will be used to evaluate the acute and long-term response of cartilage to laser irradiation. Thermal analysis (as used in materials science) will be performed to characterize cartilage temperature dependent thermal and mechanical properties, and these results will be incorporated into the FEM coupling heat transfer and viscoelastic behavior. Parametric analysis of the stress/strain field and temperature distribution to key variables and processes will be performed and used to optimize LCR in parallel with measurements of tissue viability in laser reshaped specimens. The range of laser parameters that produce effective shape change while preserving tissue viability will be determined, and estimates of phase transformation energy requirements will be calculated using the FEM. Since shape change in cartilage corresponds to stress relaxation, knowing the energy required to accelerate this process (phase transformation energy) will be a key factor in optimization since this energy deposition is largely determine by dosimetry and tissue thermal and optical properties. This proposal will focus on developing a more cogent understanding of the shape change process, and facilitate the safe transfer of LCR from the laboratory to the clinic in the U.S. Inasmuch as thermal tissue reshaping and modification is a growing topic of research, this proposal focuses on establishing the long-term mechanical behavior and fundamental physical mechanisms governing these processes in living tissues.